1. Tickets are on sale from the booking office.
(Does it mean that we can get the tickets at a reduced price?)
2. The new model goes on sale next month.
(Does this sentence mean that the new model will be sold at a reduced price next monthe?)
No. I said "on sale" USUALLY might mean at a reduced price. Not always. In these instances, it just means that the tickets or the car will be available next month or on a certain date, or at a certain place. In these instances, "for sale" and "on sale" are synonymous.
It can be confusing, I know.
The meaning must be derived from the context. For example, I cannot yet buy tickets for a hit musical that will play next fall. Season ticket holders may buy season tickets for several plays now, but individual seats will not go "on sale" until a later date. But an advertisement in today's newspaper says: "Cole Hardware Hardware Hot Deals: Sale Prices Valid Through April 30, 2016"
The tickets will not be at reduced price. The items listed in the advertisement are at "sale" or reduced prices.